1. Technical Field
The present invention relates to an encoding/transmitting apparatus and an encoding/transmitting method. More particularly, the invention relates to an apparatus and method for transmitting coded data, which are fit for use in television-meeting systems, television-telephone systems, broadcasting systems and multi-media database systems in which moving-picture data is transmitted from a transmitting side to a receiving side through a transmission path and subjected to real-time playback (streaming).
2. Background Art
In recent years, video-data converting methods are widely used in distributing data between the broadcasting stations and the households. These methods accomplish transmission and storage of data at high efficiency, by utilizing the redundancy inherent to video data when the video data is treated as digital data.
Among these video-data converting methods is an image-encoding method that is standardized by MPEG-4 (Moving Picture Expert Group). This image-encoding method is defined in ISO/IEC 14496 and is used in various applications, from those for professional use to those for consumer use.
MPEG-4 is a system that compresses moving-picture data. The MPEG-4 standards provide a system for achieving real-time playback (hereinafter called “streaming”) of moving-picture data, particularly in television-meeting systems, television-telephone systems, broadcasting systems and multi-media database systems. If data is encoded and transmitted in accordance with MPEG-4, the receiving-side system performs error correction and interleaving. Depending on the traffic condition in the transmission path, however, the packets are inevitably lost or the data inevitably has errors. To perform streaming on the network, it is, therefore, necessary to control the bit rate of the data to output and to control the amount of data passing through the transmission path.
FIG. 1 shows a conventional encoding/transmitting apparatus 100. As FIG. 1 shows, the encoding/transmitting apparatus 100 comprises a video encoding unit 101, an audio encoding unit 102, an encoded-video-data storage unit 103, an encoded-audio-data storage unit 104, and a multiplex output unit 106. The video encoding unit 101 encodes the input video data. The audio encoding unit 102 encodes the input audio data. The encoded-video-data storage unit 103 stores the video data encoded. The encoded-audio-data storage unit 104 stores the audio data encoded. The multiplex output unit 106 multiplexes the video data and the audio data, both encoded, and outputs them. The encoding/transmitting apparatus 100 further comprises a network-state determining unit 105. The network-state determining unit 105 receives information about packet loss, from the communication party. If the unit 105 determines that the load on the network is heavy, it controls the video encoding unit 101 and audio encoding unit 102 to lower the encoding bit rate.
Note that, in FIG. 1, the broken lines indicate the flow of data, and the solid lines indicate the flow of control signals.
Another method is available to control the encoding bit rate. This method is to lower the encoding bit rates of the video-data encoding unit and audio-data encoding unit, on the basis of the buffer-occupied storage areas in the data storage units. (See Japanese Patent Application Laid-Open Publication No. 11-41608.)
The encoding bit rates may be controlled in accordance with a response from the communication party. However, no response can hardly received from the communication party if congestion occurs on the network. In this case, the network-state determining unit cannot determine the state of the network. Consequently, the bit rates may not be appropriately controlled. Further, the bit rates cannot be controlled in accordance with the state of the network, by monitoring only the buffer-occupied storage areas.